ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 256 PM EDT SAT JUL 01 2017 VALID 12Z WED JUL 05 2017 - 12Z SUN JUL 09 2017 THE MAJORITY OF GUIDANCE SHOWS A SIMILAR LARGE SCALE EVOLUTION DURING THE PERIOD. MEAN RIDGING SHOULD PREVAIL OVER THE MAINLAND WHILE A SLOW MOVING UPR LOW WOBBLES TO THE SW OF THE PANHANDLE, PSBLY SHOWING SOME EWD MOVEMENT BY THE LATTER HALF OF THE PERIOD, WHILE ANOTHER UPR LOW MIGRATES INTO THE BERING SEA FROM A LATE SHORT RANGE TRACK NEAR KAMCHATKA. THERE ARE A NUMBER OF DETAIL AND TIMING UNCERTAINTIES THOUGH. OVER THE MAINLAND THE BIGGEST QUESTION MARK REVOLVES AROUND A COMPACT CLOSED LOW EXPECTED TO BE OVER THE NRN BERING SEA EARLY IN THE WEEK. BY THE START OF THE EXTENDED PERIOD AND BEYOND INDIVIDUAL MODELS AND ENSEMBLE MEMBERS ARE ALL OVER THE PLACE REGARDING THE PATH OF THIS UPR LOW, FROM N OF THE MAINLAND IN THE 06Z/12Z GFS TO THE CNTRL MAINLAND IN THE 00Z GFS WITH OTHER MODELS IN-BETWEEN. ENSEMBLE MEANS BARELY DEPICT A MERE SHRTWV DUE TO MEMBER SPREAD. TRENDS OVER THE PAST 12-24 HRS ALONG WITH 00Z UKMET/CMC/NAVGEM RUNS SUGGEST INCREASING PROBABILITY OF A FEATURE BETTER DEFINED THAN IN THE MEANS. HOWEVER IT SEEMS QUESTIONABLE TO HAVE THIS UPR LOW WITH A COMBINED DEPTH/TRACK TO THE EXTENT OF THE 00Z GFS/ECMWF GIVEN THE PREVAILING MAINLAND MEAN RIDGING. BASED ON GUIDANCE IN THROUGH THE 12Z GFS, THE BEST OPTION SEEMED TO BE INCLUDING A MODEST AMOUNT OF 00Z UKMET/CMC WITH THE 06Z GEFS/00Z ECMWF MEANS TO YIELD A DEFINED SHRTWV BUT NOT YET A CLOSED CENTER BRUSHING THE NRN MAINLAND FOR DAYS 4-5 WED-THU BEFORE OPERATIONAL SPREAD ELSEWHERE REQUIRES FULL USE OF THE MEANS. THE CORE OF THE SHRTWV WOULD TRACK JUST N OF THE NWRN COAST. REMAINING NEW 12Z SOLNS ARE AT LEAST TAKING THE MAINLAND TRACK OUT OF PLAY WITH THE NRN COAST PATH OF THE 12Z UKMET NOW THE FARTHEST S. FOR THE UPR LOW MEANDERING TO THE SW OF THE PANHANDLE, THE 00Z CMC MEAN SIDES WITH THE SLOWER GEFS MEAN RUNS VS THE 00Z ECMWF MEAN AS SOME PROGRESSION BECOMES EVIDENT LATER IN THE PERIOD. THE 00Z GFS SEEMS TO BECOME EXCESSIVELY FAST AND THE 00Z ECMWF/CMC EVENTUALLY STRAY SOMEWHAT FASTER THAN THE MEANS AS WELL. THERE IS EVIDENCE OF A FASTER TREND VS 24 HRS AGO IN THE MEANS BUT WOULD NOT WANT TO BE TOO ASSERTIVE WITH FASTER TIMING GIVEN THE GENERALLY BLOCKY NATURE OF THE PATTERN. ADJUSTMENTS MADE BY THE 12Z ECMWF/CMC PROVIDE FURTHER SUPPORT FOR LEANING AWAY FROM THE FAST SIDE OF THE SPREAD. FOR THE SYSTEM TRACKING INTO THE BERING SEA, THE 00Z ECMWF STRAYS FASTER THAN MOST OTHER CURRENT SOLNS THROUGH THE 06Z CYCLE/12Z GFS AND PRIOR CONTINUITY FROM FAIRLY EARLY IN THE FCST. THE ECMWF MEAN IS A LITTLE MORE PROGRESSIVE/NEWD THAN THE GEFS/CMC MEANS BUT AT LEAST NOT TO THE EXTENT OF THE OPERATIONAL ECMWF. IN THE NEW 12Z CYCLE THE CMC IS ON THE FASTER SIDE WHILE THE ECMWF HAS ADJUSTED SLOWER WITH THE GFS STILL IN THE MIDDLE-SLOWER CONSENSUS. BASED ON GUIDANCE COMPARISONS FOR THIS FEATURE AND THE UPR LOW OVER THE NERN PAC BY DAYS 6-8 FRI-SUN, PREFS AT THAT TIME WENT ABOUT 2/3 TOWARD THE 06Z GEFS/00Z NAEFS MEANS RELATIVE TO THE 00Z ECMWF MEAN. NOTE THAT BASED ON SOME OPERATIONAL MODEL SOLNS THERE IS POTENTIAL FOR THE MAINLAND RIDGE TO BE STRONGER THAN DEPICTED IN THE MEANS. RAUSCH